Saltwater intrusion into tidal freshwater wetlands initiates change across … · 2012-06-22 ·...

Saltwater intrusion into tidal freshwater

wetlands initiates change across multiple

levels of ecological organization

Scott C. Neubauer1, Rima B. Franklin2, Michael F. Piehler3

1 University of South Carolina, Baruch Marine Field Laboratory 2 Virginia Commonwealth University, Department of Biology 3 University of North Carolina, Institute of Marine Sciences

Marsh TypeAverage AnnualSalinity

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OceanEuhaline(Marine)

Mesohaline

Polyhaline

Oligohaline

TidalFreshwater

NontidalFreshwater

Limit of tidalinfluence

The diversity of coastal wetland

types is tremendous

Tidal freshwater marsh

Salt marsh Mangrove forest

Cypress swamp

Odum et al. 1984. FWS/OBS-83/17

Research questions

How do saltwater intrusion and altered hydrology …

… affect soil microbial processes and dynamics ?

… modify wetland plant communities ?

… impact ecosystem carbon cycling ?

… influence marsh resilience and sustainability ?

*

Atlantic coast of

North America

¿ Where am I working ?

• Brookgreen

» Tidal freshwater marsh

» 30+ herbaceous plant species

» Organic-rich soils (~60% organic, ~30% C)

» Semi-diurnal tides, doesn’t flood every tide

Experimental design

» 5 “control” plots = no manipulation

» 5 “+fresh” plots = add fresh water

» 5 “+salt” plots = add brackish water

» Started 16 June 2008, repeated ~2x per

week through 15 Nov 2011

» Add 40 L fresh or brackish water to each

+fresh and +salt plot

• freshwater from 180 m well

• brackish water is diluted seawater

» 338 water addition dates

» ~133,000 L water

¡ Salty marsh = success !

Control, +fresh, and +salt data: n = 5 plots x 2 depths (10 & 25 cm) per plot;

Ambient data: n = 2 locations x 2 depths per location

means ± std dev

Porewater

Research questions






• Microbial community structure (TRFLP, qPCR)

• Rates of CO2 and CH4 production, soil O2 demand

• Denitrification and DNRA

• Extracellular enzyme activity

Soil CO2 and CH4 production

Soil slurries mimic field salinities (S = 0

for control and +fresh; S = 2 for +salt)

Treatment means ± standard deviation, n = 5 plots per data point

Soils collected

Nov 2011

» CO2 production …

… decreases with depth

… in surface soils, is highest in control

and +fresh plots

… in deeper soils, no differences

» CH4 production …

… more variable than CO2 prod.

… shows similar depth and treatment

patterns

Aerobic–anaerobic coupling

» “Denitrification” …

… highest in control plots

… lowest in +salt plots

… driven by nitrification rather than uptake of water-

column NO3-

Net N2 production

(flux out of soil)

C > S

Whole-core incubations. Treatment means ± standard error, n = 5 plots

» Aerobic biogeochemical activity …


… ~6x higher in control plots

Soil O2 demand

(flux into soil)

C > F > S

Research questions






• Species presence/absence, richness, stem density)

• Aboveground biomass (non-destructive)

• Leaf-level photosynthesis and fluorescence

• Belowground root/rhizome biomass

Plant responses …

Bold points are treatment medians; faint symbols are for individual plots

Cicuta maculata

Spotted water hemlock

Ste

m d

ensity (

# m

-2)

(C = F) > S

+salt

+fresh control

Symphyotrichum sp.

Aster

Zizaniopsis miliacea

Giant cutgrass

… to salinity

… to freshwater •

– 1)

… to salinity

… to freshwater +

–

– 2) … to salinity

… to freshwater •

+ • 3)

F > C > S

+salt

+fresh

control

S > (C=F)

+salt

+fresh control

Community richness and biomass

» Freshwater inputs increased total*

biomass

» Elevated salinity decreased total*

biomass

» Total* biomass ~85% of total plot

biomass (range: 42-97%, 5 external

plots each in Aug and Sep 2011; all

treatment plots in Nov 2011)

Species richness Total* biomass

» Salinity reduced species richness

by 50-75%

» Richness was slightly lower in

+fresh plots relative to controls

Points are means ± standard deviation, n = 5 plots per data point.

C > F > S F > C > S

Research questions






• Gross ecosystem production

• Ecosystem CO2 and CH4 emissions

• Net ecosystem production

• Soil C/N inventories, 137Cs accretion

Ecosystem carbon fluxes

» Marsh-atmosphere CO2 and CH4 exchanges … temperature-controlled chambers

… ~ monthly from May 2008 thru Nov 2011

» Modeled monthly and annual fluxes … photosynthesis vs. light curves

… respiration vs. temperature relationships

… weather data

Annual flux summary

» Gross ecosystem production … consistently lowest in +salt treatment

… similar between control and +fresh plots

» Ecosystem respiration … CO2 and CH4: lowest in +salt treatment

… CO2

• 2008/09: higher in control than +fresh

• 2010/11: similar in control and +fresh

… CH4 generally similar in control and +fresh

» Net ecosystem production … positive in all treatments and all years

… lowest in +salt treatment in some years, but

not others

Thanks!

BMFL/USC

• Amanda Rotella

• Rebecca Schwartz

• Liana Nichols

• Olivia De Meo

• Paul Kenny

• Stephen Forehand

• Seth Stewart

UNC – IMS

• Ashley Smyth

VCU

• David Berrier

• Ember Morrissey

• Jaimie Gillespie

• Bonnie Brown

• Leigh McCallister

• Lindsey Koren

VIMS

• Lori Sutter

Other

• Tom Marshall

• Shan Deeter

• Troy Washam

• Michelle, Isabella, Ryleigh Neubauer

• Dorothy Silvernail

• staff of Brookgreen Gardens

Drivers of ecosystem processes

» Tight coupling between CH4 emissions

and precipitation … rainfall affects soil oxygenation?

… effect of freshwater additions greatest in drier

years

… emissions from +salt plots consistently low

» “Rainfall effect” not seen in CO2 fluxes … greatest effect of freshwater additions in

cooler years (2008/2009)

… temperature x treatment interaction?

2008, 2009: 26.3°C

2010, 2011: 27.2°C

Average summer temp.

Disturbance effects across scales

Microbes

Biogeochemical activity

CO2 production:

CH4 production:

Denitrification:

Plants

Community

Richness:

Biomass:

Density:

Biomass:

Populations

Ecosystem functioning

CO2 fixation:

CO2 emissions:

CH4 emissions:

Net ecosystem production:

Incre

ased f

resh

wate

r in

puts

+ +

•

– • + • • + •

–

+

• • –

• • –

• • •

• + •

Environm

enta

l change

Disturbance effects across scales

Microbes

Biogeochemical activity

CO2 production:

CH4 production:

Denitrification:

Plants

Community

Richness:

Biomass:

Density:

Biomass:

Populations

Ecosystem functioning

CO2 fixation:

CO2 emissions:

CH4 emissions:

Net ecosystem production:

Saltw

ate

r in

trusio

n

+

–

–

–

– – • + – – •

– –

– – –

– – –

– – –

– – •

Change in flux

Time scale CO2 production CH4 production

Soil CO2 and CH4 production

3-8 cm soil layer, bars are treatment medians; symbols are values for each plot.

Experiment #2:

Incubate soils at multiple salinities (S = 0, 2, 5)

Short-term (no effect) 96% decrease

Long-term 60% decrease 85% decrease

Gross ecosystem production

(median model results with bars indicating 25th-75th percentiles)

(2008 and 2009 data in Neubauer, Online First article, Estuaries and Coasts)

» Initially, gross ecosystem production initially higher in +salt plots

» During last 3 years, GEP consistently lower in +salt plots than in

other treatments

Ecosystem respiration



» Growing season CO2 emissions higher in control and +fresh plots

» Summer peak in CH4 emissions not as pronounced in +salt plots

» Respiration is dominated by non-methanogenic pathways,

regardless of treatment.

Net ecosystem production



Soil enzyme activity

Treatment means ± standard error, n = 5.

Soils collected Nov 2011

» No treatment differences in “labile”

enzyme activity

» Considerably lower activity of enzymes for

degrading “recalcitrant’ lignin in +salt plots

Data from RB Franklin.

Enzymes for degrading cellulose

… ß-glucosidase, cellobiosidase

Enzymes for degrading lignin

… phenol oxidase, peroxidase

“labile”

“recalcitrant”

» Patterns may reflect inhibition of phenol oxidase and peroxidase by

… low O2 ?

… salt ?

… sulfide ?

» Similar patterns at 8-13 cm, but few

differences at 23-28 cm

“recalc

itra

nt”

“labile”

Photosynthesis and fluorescence

P. virginica (Apr 2011) Z. miliacea (Oct 2011)

Peltandra virginica

» Increased water inputs decreased leaf photosynthesis by 60%

» Salinity decreased photosynthesis by another 35%

Zizaniopsis miliacea

» No effect of salinity or increased water inputs on …

… leaf photosynthesis

… leaf fluorescence

C > F > S

n.s.

n.s.

Data from LA Sutter, VIMS

Microbial community composition

Surface soils collected Oct 2009

» DNA fingerprinting (TRFLP)

… significant community shifts due to saltwater

intrusion

» Do communities vary with depth?

» Have there been additional changes in

community composition over time?

Aerobic and anaerobic activity

» Aerobic biogeochemical activity …


… ~6x higher in control plots

Soil O2 demand

(flux into soil)

» Both aerobic and anaerobic activity

show similar treatment differences …

… but only in near-surface soils

… no correlation in deeper soils

C > F > S

Whole-core incubations. Treatment means ± standard error, n = 5 plots per column.

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Saltwater intrusion into tidal freshwater wetlands initiates change across … · 2012-06-22 ·...

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